Flip chip package, circuit board thereof and packaging method thereof

ABSTRACT

According to the present invention, when a semiconductor element having protruding electrodes formed thereon is connected to a circuit board via conductive resin, stable connection is made even when an electrode pitch is small on the semiconductor element. On semiconductor element package regions on the circuit board, a paste electrode material containing photopolymerizable materials is printed to form a film having a prescribed thickness, and this electrode material film is baked after exposure and development thereof so as to obtain circuit electrodes having edges warped in a direction of going apart from the circuit board surface. Then, the protruding electrodes and the concave surfaces of the circuit electrodes are brought in abutment with each other and connected via the conductive resin which surrounds the abutments between the respective electrodes and is held on the concave surfaces of the circuit electrodes. With this arrangement, the concave surfaces of the circuit electrodes act as saucers and prevent the conductive resin from being squeezed out, thereby eliminating possible occurrence of short circuits.

TECHNICAL FIELD

[0001] The present invention relates to a flip chip package, a circuitboard thereof and a packaging method thereof, and specifically to a flipchip package having an electrode structure suitable for a flip chippackage, a circuit board thereof and a packaging method thereof.

BACKGROUND ART

[0002] An electronic circuit has been recently higher in density, andthe need for a smaller area and connecting resistance has beenintensified regarding a packaged device. One of means for attaining ahigh-density package is flip chip package. Several kinds of packagingmethods are available for the flip chip package, and in consideration ofeasy repair and unleading, which has attracted attention in recentyears, SBB method (Stud Bump Bonding) is a desirable technique. The SBBmethod is a technique for forming protruding electrodes, which are madeof materials such as Au, on a semiconductor element by a wire bondingmethod and for connecting the protruding electrodes and electrodes on acircuit board via conductive resin.

[0003] Referring to FIG. 3, a paste electrode material is firstlyprinted on a circuit board 11 by a method such as screen printing, andthe circuit board 11 is baked at a temperature of sintering theelectrode material. Thus, circuit electrodes 12 are formed on thecircuit board 11. On the other hand, protruding electrodes 14 are formedon a semiconductor element 13 by a method such as wire bonding, and alayer of conductive resin 15 is formed on the protruding electrodes 14by transferring and so on. Thereafter, the circuit board 11 and thesemiconductor element 13 are positioned high accurately and a suitableload is applied thereon. Hence, the semiconductor element 13 is packagedon the circuit board 11.

[0004] However, the above conventional packaging method isdisadvantageous as in the following. First, since the semiconductorelement 13 has decreased in electrode pitch in recent years, anelectrode pitch on the circuit board 11 needs to be smaller accordingly.However, according to the conventional screen printing method, a pitchis limited up to 300 μm and printing is difficult with a pitch below thelimit, causing frequent short circuits and breaks in a wire.Consequently, the yields are lowered.

[0005] Secondly, when the semiconductor element 13 is smaller inelectrode pitch, it is quite difficult to control a quantity of theconductive resin 15 transferred onto the protruding electrodes 14 of thesemiconductor element 13. Particularly, short circuits are more likelyto occur. In order to prevent the short circuits, a quantity of theconductive resin 15 is set smaller than that of the conventional art.However, since the electrode material expands laterally, the circuitelectrodes 12 are each half-round in cross section when an electrodepitch is 100 μm. In the case where flip-chip packaging is carried out onthe circuit electrodes 12, the conductive resin 15 is squeezed out ofthe circuit electrodes 12 as shown in FIG. 3. Therefore, the conductiveresin 15, which is squeezed out of the adjacent circuit electrodes 12,may be short-circuited.

DISCLOSURE OF INVENTION

[0006] The object of the present invention is to make a stableconnection with a circuit board even when a semiconductor element has asmall electrode pitch.

[0007] In order to solve the foregoing problem, when protrudingelectrodes formed on the semiconductor element are connected to circuitelectrodes on the circuit board via conductive resin, the presentinvention comprises the steps:

[0008] (a) forming an electrode material film having a prescribed dryfilm thickness by using a paste electrode material containing aphotopolymerizable material;

[0009] (b) exposing and developing the electrode material film;

[0010] (c) baking the developed electrode material film; and

[0011] (d) flip-chip packaging the semiconductor element on the circuitelectrodes formed in the above steps.

[0012] In the above steps, concave circuit electrodes having warpededges are formed on the circuit board. Since the concave surfaces of thecircuit electrodes act as saucers, it is possible to flip-chip packagethe semiconductor element without squeezing out any conductive resin.Consequently, it is possible to eliminate the occurrence of shortcircuits, achieving a reliable packaging for the semiconductor element.

[0013] Ceramic is applicable as the circuit board. The circuit board,can be provided not only with a circuit including circuit electrodes formounting the above semiconductor element, but also a circuit formounting components other than the semiconductor element as well as acircuit for making connection with another board.

[0014] Such an electrode material is used that contains, at least,metallic materials such as Au, Ag, or Cu and glass as inorganiccomponents, and a monomer and a polymer which also serve as polymericmaterials and a photoinitiator as organic components. Ni or Au platingmay be applied to the surface of the formed circuit electrodes.

[0015] Such a semiconductor element is used that is formed with theprotruding electrodes made of metallic materials such as Au, Al, Cu, andsolder. Any method including wire bonding and plating is applicable forforming the protruding electrodes.

[0016] The conductive resin is applicable as long as the resin containsconductive components such as Au, Ag, and Cu to connect the protrudingelectrodes on the semiconductor element and the circuit electrodes onthe circuit board. Any type of resin is applicable regardless of whetherit is thermosetting or thermoplastic.

[0017] In the above step (a), a film is formed by printing a pasteelectrode material on the circuit board. The electrode material needs tobe printed only on a package region for packaging the semiconductorelement. The other regions may be formed with a circuit pattern inadvance according to the above mentioned conventional method. Inaddition, upon printing, which is not intended for forming a circuitpattern, printing may be performed over, the entire surface of thepackage region. Thus, a rough printing such as a conventional screenprinting is sufficiently applicable. The electrode materials is dried ata suitable temperature to prevent the material from flowing afterprinting. However, a printing plate and printing conditions need be setso as to secure a prescribed film thickness, which is preferably 10 to20 (μm).

[0018] In step (b), a glass mask and so on are positioned on the circuitboard, on which the electrode material is printed and dried. The glassmask is formed, such that only an electrode region having thesemiconductor element transmits light. Ultraviolet rays having awavelength of 320 to 370 nm are radiated at 300 to 500 mJ. Thereby,polymeric materials on an electrode region which transmits ultravioletrays are started by a photoinitiator to react and polymerized. Aftersome appropriate time, the board is entirely developed by means of asolution for dissolving a polymeric material which has not reacted.Thus, the film is removed from other parts than the electrode regionsand remains on the electrode regions. At this time, by adjusting thefilm-thickness, polymeric materials receiving less light are left toremain insufficiently polymerized toward the board. Upon development,erosion is started from non-electrode regions from which the film hasbeen removed, further to wider area toward the board. As a result, thefilm has a trapezoidal cross section on the electrode region. When afilm thickness is small, all the polymeric materials are polymerized andit is impossible to obtain a film having a trapezoidal cross section.Therefore, the above film thickness is demanded.

[0019] In step (c), the circuit board completed with exposure anddevelopment is baked at a temperature for sintering the electrodematerial, and the circuit electrodes are baked onto the circuit board.At this time, the electrode material film is caused to slightly shrink,so that both ends of the formed circuit electrode are slightly warped(such warped part is called an edge curl) and the cross section of thecircuit electrode becomes arc-shaped. Plating of Ni, Au and so on may beapplied in order to protect the electrode surfaces after baking.

[0020] In step (d), the semiconductor element having the protrudingelectrodes formed thereon is flip-chip packaged on the circuit board byusing the conductive resin. At this time, the edge curl of the circuitelectrode acts as a wall, thereby, preventing the conductive resin frombeing squeezed out.

BRIEF DESCRIPTION OF DRAWINGS

[0021]FIG. 1 is a process sectional view explaining a method offlip-chip packaging a semiconductor element according to Embodiment 1 ofthe present invention;

[0022]FIG. 2 is a process sectional view explaining a method offlip-chip packaging a semiconductor element according to Embodiment 2 ofthe present invention; and

[0023]FIG. 3 is a process sectional view explaining a conventionalmethod of flip-chip packaging the semiconductor element.

BEST MODE FOR CARRYING OUT THE INVENTION

[0024] The present invention is characterized in that when asemiconductor element is flip-chip packaged on a circuit board by usinga conductive resin, the element having protruding electrodes formedthereon, an electrode material containing photopolymerizable materialsis printed on a semiconductor element package region on the circuitboard such that a film is formed with a prescribed thickness, concavecircuit electrodes are formed by baking the electrode material filmafter exposure and development are performed so as to allow theelectrode material film to remain only on prescribed electrode regions,the concave circuit electrode having edges warped in a direction ofgoing apart from a board surface, the protruding electrodes formed onthe semiconductor element are brought into contact with the concavesides of the concave circuit electrodes, and the protruding electrodesand the circuit electrodes are connected with each other via theconductive resin. Further, the present invention is characterized byforming the electrode material film with a dry film thickness of 10 to20 micrometers by using a flip-chip packaging method.

[0025] Moreover, the present invention is characterized in that theelectrode material film remaining after development is trapezoidal incross section that is wider as it goes farther from the circuit board.

[0026] Also, the present invention is characterized in that the circuitelectrode is arc-shaped in cross section according to the flip-chippackaging method.

[0027] Besides, according to the present invention, a flip-chip package,in which the semiconductor element having the protruding electrodesformed thereon is packaged on the circuit board by using the conductiveresin, is characterized in that the circuit board includes the concavecircuit, electrodes each having edges warped in a direction of goingapart from the board surface, the semiconductor element is disposed suchthat the ends of the protruding electrodes are in contact with theconcave surfaces of the concave circuit electrodes, and the protrudingelectrodes and the circuit electrodes are, connected to each other viathe conductive resin.

[0028] Furthermore, according to the present invention, the circuitboard for flip-chip packaging the semiconductor element, which has theprotruding electrodes formed thereon, by using the conductive resin, ischaracterized by including the concave circuit electrodes each havingedges warped in a direction of going apart from the board surface.

[0029] Referring to drawings, the embodiments of the present inventionwill be discussed in a specific manner.

[0030]FIG. 1 is a process sectional view explaining a method ofpackaging a semiconductor element according, to Embodiment 1 of thepresent invention.

[0031] As shown in FIG. 1(a), a paste electrode material 2 containingphotopolymerizable materials is printed on an area for placing asemiconductor element on a circuit boards 1. After printing, theelectrode material 2 is dried at a suitable temperature without flowing.At this moment, the electrode material 2 is printed while sprinting typeand conditions are determined so as, to have a film thickness of 10 to20 μm after drying.

[0032] Then, as shown in FIG 1(b), a glass mask 3 is disposed on thefilm of the electrode material 2 while being positioned on the circuitboard 1. Openings 3 a are formed on the glass mask 3 to transmit lightthrough a desired circuit pattern. To be specific, the 50 μm-widthopenings 3 a corresponding to electrode regions are formed with a 100μm-pitch. Then, UV (ultraviolet ray), having a wavelength of 320 to 370nm is radiated at 300 to 500 mJ from the above of the glass mask 3.

[0033] As shown in FIG. 1(c), due to UV passing through the openings 3a, photopolymerizable materials of the electrode material 2 on theelectrode regions 2 a, i.e., a photoinitiator, a monomer, and a polymerare reacted with one another to proceed polymerization. In contrast,regarding photopolymerizable materials of the electrode material 2 onnon-electrode regions 2 b, polymerization does not occur. Since UV isnot likely to enter the neighborhood of the circuit board 1, theelectrode materials 2 are not likely to be ppolymerized on-theseregions.

[0034] Subsequently, the electrode material 2 is developed by using analkaline solution and so on. Thus, it is-possible to dissolve and removethe electrode material 2 on the non-electrode regions 2 b having nopolymerization or insufficient polymerization. As shown in FIG. 1(d),this operation removes the electrode material 2 on the non-electroderegions 2 b. In the vicinity of the surface of the electrode material 2on the electrode regions 2 a, polymerization is proceeded completely.Hence, the electrode material 2 remains without any erosion so as tocorrespond in shape to the openings 3 a of the glass mask 3. Meanwhile,regarding the electrode material 2 around the circuit board 1,polymerization is not completed over a wide region as compared with theneighborhood of the surface, resulting in erosion larger than theopenings 3 a. Consequently, the electrode material 2 on the electroderegion 2 a is trapezoidal in cross section,. Thereafter, since thecircuit board 1 is baked at a temperature of sintering the electrodematerial 2 as shown in FIG. 1(e), the electrode material 2 on thecircuit board 1 is baked as circuit electrodes 4. According to FIG.1(e), since the electrode material 2 contracts upon baking, the edges ofthe circuit electrodes 4 are warped in a direction of going apart fromthe circuit boards (edge curl), and the circuit electrodes 4 arearc-shaped depressions in cross section.

[0035] Finally, as shown in FIG. 1(f), the semiconductor element 7, onwhich conductive resin 6 is transferred to protruding electrodes 5, isaccurately positioned to the circuit substrate 1 such that theprotruding electrodes 5 and the circuit electrodes 4 are opposed to eachother. A suitable load is applied to the semiconductor element 7, theprotruding electrodes 5 and the circuit electrodes 4 are brought intocontact with each other, and the conductive resin 6 is cured. Hence, theflip chip packaging of the semiconductor element 7 is completed.

[0036] In the flip chip package manufactured in the above manner, theedge-curled circuit electrodes 4 prevent the conductive resin 6 frombeing squeezed out of the circuit electrodes 4. Therefore, at the timeof packaging the semiconductor element 7 with a 100-μm electrode pitch,the conductive resin 6 expanding laterally does not cause any shortcircuits between the adjacent electrodes.

[0037] Now, the circuit electrodes 4 will be further discussed.

[0038] As shown in FIG. 1(e), a maximum distance from the surface of thecircuit board 1 to the edge-curled circuit electrodes 4 is defined as anedge curl amount L-(see FIG. 1(e)). An edge curl amount L isconsiderably dependent upon a dry film thickness of the electrodematerial 2 shown in FIG. 1(a). When a dry film thickness is 10 to 20 μm,an edge curl amount L is 2 to 10 μm. Thus, the circuit electrodes 4 canact as saucers.

[0039] Meanwhile, when a dry film thickness is larger than 20 μm, partsnot being polymerized on the circuit board 1 are larger in thickness,and the electrode material 2 to be developed and removed on the circuitboard 1 remains resulting in short circuits. In contrast, when a dryfilm thickness is 10 μm or less, an edge curl amount L is 2 μm or lessand the circuit electrodes 4 cannot sufficiently, act as saucers.

[0040]FIG. 2 is a process sectional view explaining a method ofpackaging a semiconductor element according to Embodiment 2 of thepresent invention.

[0041] As shown in FIG. 2(a), like Embodiment 1, edge-curled circuitelectrodes 4 are formed on a circuit substrate 1. And then a mask (notshown) having openings corresponding to the circuit electrodes 4 ispositioned onto the circuit electrodes 4, and conductive resin 6 isapplied to the circuit electrodes 4 as shown in FIG. 2(b) by using aprinting method and so on. Thereafter, as shown in FIG. 2(c), asemiconductor element 7 having protruding electrodes 5 formed thereon ispositioned to the circuit board 1, and a suitable load is applied ontothe semiconductor element 7. Hence, the flip chip packaging of thesemiconductor element 7 is completed.

[0042] According to such a method as well, like Embodiment 1, theedge-curled circuit electrodes 4 act as saucers to prevent theconductive resin 6 from being squeezed out, thereby eliminating theoccurrence of short circuits.

EXPERIMENTAL EXAMPLE

[0043] A semiconductor element is packaged according to the Pi abovemanufacturing steps and the performance is evaluated. Used members andmaterials are:

[0044] circuit board: low-temperature baked ceramic

[0045] multilayered board (test pattern)

[0046] board size: 30×30×0.65 (mm)

[0047] electrode pitch: 100 (μm)

[0048] number of electrodes: 360 pins

[0049] The electrode material 2 contains Ag as a-metallic component witha dry film thickness of about 15 μm. And then, the electrode materialfilm is exposed and developed using a glass mask having openings formedthereon. The openings are each about 50 μm in width. The electrodematerial 2 on the non-electrode regions 2 b having no or insufficientpolymerization is dissolved and removed. The circuit board 1, on whichthe electrode material 2 on the non-electrode regions 2 b is dissolvedand removed, is baked at about 800 to 1000° C. Hence, the electrodematerial 2 on the circuit board 1 is baked as circuit electrodes 4. Atthis moment, an edge curl amount L is 4 μm. Ni plating and Au platingare applied to protect the surface.

[0050] IC: Dummy IC

[0051] IC size 10×10×0.5 (mm)

[0052] IC electrode pad pitch: 100 (μm)

[0053] Number of pins: 360 pins

[0054] The protruding electrodes 5 are formed on the electrodes of theabove IC by using metallic wires, and the conductive resin 6 istransferred onto the formed protruding electrodes 5. The conductiveresin 6 contains Ag as a metallic component and epoxy as a resincomponent. The IC including the conductive resin 6 is positioned ontothe circuit board 1 and a weight of several grams is applied to each ofthe protruding electrodes so as to complete packaging. And then, aftercuring the conductive resin 6 by heating, evaluation is made onshort/open. FIG. 1 shows the result. TABLE 1 Method of Present Open 0/5Package Invention Short 0/5 Package Conventional Method Open 0/5 PackageShort 4/5 Package

[0055] As understood from Table 1, the method of the present inventiondoes not cause any opens or short circuits at all. Meanwhile, theconventional method causes short circuits on a ⅘ package. Thus, theeffectiveness of the present invention can be confirmed.

[0056] As described above, according to the present invention, theedge-curled circuit electrodes are formed on the circuit board, and theprotruding electrodes of the semiconductor element are connected to thecircuit electrodes by using the conductive resin. Hence, it is possibleto prevent the conductive resin from being squeezed out while thecircuit electrodes act as saucers, achieving a reliable packaging forthe semiconductor element without any occurrence of short circuits.

1. A flip-chip packaging method, wherein in flip-chip packaging asemiconductor element on a circuit board by using conductive resin, saidelement having protruding electrodes formed thereon, the methodcomprising: printing an electrode material containing photopolymerizablematerials on a semiconductor element package region on said circuitboard such that a film is formed with a prescribed thickness, andforming concave circuit electrodes by baking said electrode materialfilm after performing exposure and development of said electrodematerial film to allow said electrode material film to remain only onprescribed electrode regions, thereby forming concave circuit electrodeshaving edges warped in a direction of going apart from the circuit boardsurface; and bringing said protruding electrodes formed on saidsemiconductor element into abutment with concave faces of said concavecircuit electrodes, and connecting said protruding electrodes and saidcircuit electrodes with each other via the conductive resin.
 2. Theflip-chip packaging method according to claim 1, wherein said electrodematerial film is formed to have a dry film thickness of 10 to 20micrometers.
 3. The flip-chip packaging method according to claim 1 or2, wherein said electrode material film remaining after development istrapezoidal in cross section that is wider as it goes farther away fromsaid circuit board.
 4. The flip-chip packaging method according to claim1 or 2, wherein said circuit electrode is arc-shaped in cross section.5. A flip-chip package in which a semiconductor element havingprotruding electrodes formed thereon is packaged on a circuit board byusing conductive resin, wherein said circuit board includes concavecircuit electrodes each having edges warped in a direction of goingapart from the circuit board surface, said semiconductor element isdisposed such that ends of said protruding electrodes thereof come inabutment with concave surfaces of said concave circuit electrodes, andsaid protruding electrodes and said circuit electrodes are connected toeach other via the conductive resin.
 6. A circuit board for flip-chippackaging a semiconductor element by using conductive resin, saidelement having protruding electrodes formed thereon, comprising concave,circuit electrodes each having edges warped in a direction of goingapart from the circuit board surface.